Comparative Study On Geochemistry And Hydrocarbon Potential Of Lacustrine Black Mudstones

The northeast uplift belt is affected by tectonic uplift,and it is affected by denudation for a long time.The loss of stratum is common.The oil and gas exploration in this block has been at a low level.In recent years,with the advancement of exploration technology of dense oil and gas and the deepening of field survey work,the research on tight oil layers in this area has attracted extensive attention from scholars at home and abroad.At present,there are differences in the mineralogical characteristics,geochemical characteristics,hydrocarbon generation potential and other indicators between the black mudstone with tuffaceous debris and the black mudstone with no tuffaceous debris involved in the Chang 7 Member of the Yanchang Formation.The comparative study is still in a blank stage and it is impossible to further explore the relationship between high-quality tight oil layers and tuff debris.On the basis of previous studies,this dissertation makes a more detailed lithology of member 7₃ of Yanchang Formation in Tongchuan area,southeast Erdos Basin.Two types of samples are selected to study the geochemistry and hydrocarbon generation potential differences.Samples of black mudstone,composed of terrigenous and volcanic clastics,showing extreme fine-grained texture and with high content of tuffaceous material were taken from Xiaoqiaohe and Motiangou of Tongchuan area and samples of black–gray mudstone,composed of extremely fine-grained terrigenous clastics,almost with no tuffaceous or volcanic material,were taken from Yangjichang in Yichuan area,which is in northeast of Tongchuan area.Five conclusions are drawn based on comparison in petrology,geochemistry and hydrocarbon generation potential between two types of samples:1.The black tuffaceous mudstone can be classified into gray-white thin–extremely thin laminated,medium-fine-grained tuffaceous stone?GMT?and black thin-extremely thin laminated mudstone composed of fine–grained terrigenous clastics and volcanic clastics?BFM?.2.REE pattern of GMT and BFM indicates crustal genesis and their similarity suggest some kind of affinity.3.Geochemistry results show paleoaquatic environment of BFM and samples of Yichuan area is freshwater,while ones of Tongchuan area was under more reducing environment while with lower ability of paleoproductivity.4.Rock pyrolysis data show BFM with organic type of?₁ has much higher organic matter abundance than samples with organic type of?in Yichuan area.Organic matter in former samples are in low mature stage while organic matter in latter samples are in mature stage.Thus BFM with organic type of?₁ has huge hydrocarbon generation potential.5.Based on petrology,mineralogy and geochemistry study of tuffaceous material in black mudstone of member 7₃,this dissertation put up an ideal sedimentary model of how volcanic material involved in deposition after they fell into lake.